Plants root respiration

The partial pressure of C02 in the soil air controls the concentration of both dissolved C02 and undissociated carbonic acid. At 0.003 atm of C02 (g) as a reference level for soils, [H2C03°] is about 1.04 x 10 4 M (Lindsay, 1979). At a normal atmospheric level of 0.0003 atm C02 (g), [H2C03°] is approximately 1.04 x 10 5 M. In most soils, C02 (g) is higher than in the atmosphere. C02 is released from soil and plant root respiration. In flooded soils, C02 (g) partial pressure increases to 0.01-0.3 atm, about 1000-fold higher than normal upland soils due to strong microbiological activity (Lindsay, 1979). 

Finally, we consider acidification mechanisms specific to the continents so that ocean acidification is not an issue. Both enhanced respiration by surviving plant roots and bacterial decomposition of dead biomass witliin soils following Uie impact may have increased soil carbonic acid concentrations and soil weathering. (Dead biomass is also a source of alkalinity as Ca and other cations are released into the soil solution, but this process neutralized only a fraction of Uie total carbonic acid produced.) The subsurface soil biomass presently contains 2 x 10 moles C, which, if multiplied by -4 in the late Cretaceous, may liave been able to supply just enough carbonic acid to explain the foram Sr data. However, nearly all of the subsurface soil biomass would liave to have been decomposed by bacteria. Furthermore, the vast majority of CO2 released in soils diffuses out of the soil and joins the atmosphere [27], The numbers for plant root respiration are even less favorable. Presently, respiration accounts for 0.5 X 10 mol C yr released in soils. In the post-K/T impact atmosphere photosyntliesis was very likely interrupted for at least several months by dust and aerosols [7,8], so surviving plants would have had to respire at four times present biomass. One year of respiration yielded 2 x 10 mol CO2, not enough to weather Sr even if the CO2 remained in the soil. 

Carbon. Two sources of carbon are generally recognized as contributing to the carbon load of groundwaters (1) the CO2 present in the soil atmosphere that is derived from plant root respiration and decay of organic matter and... 

Several authors have applied in situ pulse labeling of plants (grasses and crops) with C-CO2 under field conditions with the objective of quantifying the gross annual fluxes of carbon (net assimilation, shoot and root turnover, and decomposition) in production grasslands and so assess the net input of carbon (total input minus root respiration minus microbial respiration on the basis of rhizodeposition and soil organic matter) and carbon fixation in soil under ambient climatic conditions in the field. 

Tolley MD, DeLaune RD, Patrick WH. The effect of sediment redox potential and soil acidity on nitrogen uptake, anaerobic root respiration, and growth of rice (Oryza saliva). Plant Soil. 1986 93 323-331. 

Two general approaches, component integration and whole system analysis have been used for to assess soil and root respiration (Anderson 1982 Hanson et al. 2000 Bostrom et al. 2007). In component integration the net respiration is determined by summing the respiration rates of the individual components (roots, plant residues, and soil). The disadvantage of this approach is the physical separation of these materials and that interactions between components cannot be evaluated. 

The greater the amount of carbon dioxide in soil, the more hydronium ions and so the lower the pH. Soil that has a low pH is referred to as sour. (Recall from Chapter 10 that many acidic foods, such as lemon, are characteristically sour.) Two main sources of soil carbon dioxide are humus and plant roots. The humus releases carbon dioxide as it decays, and plant roots release carbon dioxide as a product of cellular respiration. A healthy soil may have enough carbon dioxide released from these processes to give a pH range from about 4 to 7- If the soil becomes too acidic, a weak base, such as calcium carbonate (known as lime or limestone), can be added. 

Despite its importance in ecosystem C fluxes, soil respiration has limitations as a constraint on SOM turnover, for two main reasons. First, it is difficult to partition soil respiration into its two sources (1) decomposition of SOM by microbes (heterotrophic respiration) and (2) respiration from live plant roots (autotrophic respiration) (Kuzyakov, 2006). As a result, an increase in soil respiration may indicate not only an increase in SOM decomposition but also an increase in root respiration. Second, it is likely that in most soils only a small fraction of total SOM contributes to heterotrophic respiration. As a result, respiration measurements provide information about the dynamic fraction of SOM (particularly when combined with 14C measurements of respiration) but do not provide information about the large, stable pools unless they are destabilized and contribute to respiration (detectable with 14C02 respiration measurements). Attributing the sources of respiration from different SOM reservoirs, which may respond differently to climatic variables, is not... 

Kuzyakov, Y., and Siniakina, S. V. (2001). Siphon method of separating root-derived organic compounds from root respiration in non-sterile soil. J. Plant Nutr. Soil Sci. 164, 511-517. 

Now we must attempt to determine the source of the rest of the HCO3 in river waters. The HCO3 is derived from two major sources atmospheric CO2 that has interacted directly with silicate minerals or has been incorporated into plants by photosynthesis, later to be released by plant decay or root respiration and CO2 produced by oxidation of fossil carbon already present in rocks (Garrels and Mackenzie, 1971a, 1972 Holland, 1978). 

H20 Aerobic respiration +820 Animals, plants roots, fungi, aerobic bacteria... 

Almost all physiological processes in plants take place in the presence of water. Essential anabolic reactions (photosynthesis, assimilation, and protein synthesis), and catabolic ones (respiration and hydrolysis) occur in an aqueous cellular environment. Essential elements absorbed by plant roots, and the foods and other metabolites manufactured by the leaves and other tissues, move in aqueous solution from the regions of absorption or manufacture to other parts of the plant where additional anabolic reactions and ultimate food storage take place. Water is the major constituent of protoplasm, and is particularly abundant in young and growing tissues. 

The concentration of C02 in the atmosphere is 0.03% by volume. In the soil air, that is, the air between the soil grains, the concentration of C02 is 50 to 100 times higher. The source of the extra C02 is biogenic respiration of plant roots and bacterial decomposition of buried plant remains. 

Rain and surface water dissolve small amounts of atmospheric C02. Significantly more C02 is added to water percolating through the soil layer, as soil air contains about 100 times more C02 as compared to free air. Soil C02 is produced by biological action such as root respiration and decay of plant material. This C02 was tagged by the atmospheric 14C concentrations, that is, about 100 pmc in pre nuclear bomb times (pre-1952) and up to 200 pmc in post-bomb years. 

The atmosphere is a major source of soil acidity. Even in unpolluted environments rainwater is slightly acidic, having a pH of about 5.7 due to the dissolution of atmospheric CO2 to form the weak carbonic acid (see Worked example 5.4). The CO2 concentration in the partially enclosed soil pore system can be significantly higher (typically up to about 10 times) than in the free atmosphere due to respiration of soil microorganisms and plant roots. This results in a lower pH. In areas affected by industrial pollution, sulfur dioxide and nitrogen oxides dissolve in rainwater to produce sulfuric and nitric acids (acid rain), which are both strong acids and cause even more acidity. 

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